Hydraulic motor system and cooling means for the pump thereof



July 17, 1951 T. F.

HYDRAULIC MOTOR SYS STACY 2,560,749 TEM AND COOLING MEANS FOR THE PUMPTHEREOF Fild May 27, 1944 2 Sheets-Sheet l Fiaw v ggzzzaior July 17,1951 T. F. STACY 2,560,749

HYDRAULIC MOTOR SYSTEM AND COOLING MEANS FOR THE PUMP THEREOF Filed May27, 1944 2 Sheets-Sheet 2 Patented July 17, 1951 HYDRAULIC MOTOR SYSTEMAND COOLING MEANS FOR THE PUMP THEREOF Thomas F. Stacy, Piqua, Ohio,assignor to The French Oil Mill Machinery Company, Piqua,

Ohio

Application May 27, 1944, Serial No. 537,565

14 Claims. 1

This invention relates to hydraulic motors and is in the nature of animprovement upon my prior depending application, Serial No. 492,526,filed June 28, 1943, to which reference may be had for a more completedisclosure of the hydraulic motor and an operating system therefor.

In operating systems for hydraulic motors, such as presses, variabledelivery pumps are extensive- 1y employed for supplying the operatingfluid to the motors, and such pumps are frequently operating undersubstantial pressures for substantial periods of time, which tends tocause heating of the operating oil and of the main pump, particularly ifthe rate of delivery or fluid flow through that pump is curtailed to asubstantial extent.

One of the objects of the invention is to provide improved means forcooling the main pump in a manner to prevent it from overheating andthereby to reduce wear on the parts of the pump, and to prevent anundesired temperature rise in the operating oil or fluid for thehydraulic motor.

In modern hydraulic presses, it is becoming quite common practice todispose the reservoir at the top of the press, and many of the operatingand control equipment and parts, suchas valves, pumps, and othermechanism of the controls within, or above the reservoir for surplus"operatingfiuid or oil, and also to include within or Just above thereservoir as many as possible ofthe pipes and connections between thepump, the valves and the controls, so that leakage will always be intothe reservoir, where it will be harmless. i

' Another object of the invention is to provide an improved arrangementby which access may be easily had to the valves, pumps, pipes and othermechanism within a reservoir when servicing of those parts is necessary,andwith which thereservoir may be easily and quickly emptied or refilledin a simple manner, and without extra pumps and apparatus wheneverdesired.

Another object of the-invention isto provide an improved operatingsystem for a hydraulic motor by which overheating of the main pump maybe prevented; with which a pilot fluid under pressure will be availablewith a desired minimum pressure at all times to operate controls for thehydraulic motor with which the valves,' pumps and other operating partsand much of the piping may be disposed within or just above a reservoirfor the operating fluid, and such pipes, valves and pumps made easilyaccessible for servicing and repairs whenever necessary and which willutilize a minimum of apparatus and parts.

Another-object of the invention is-toprovide improved means by whichmuch of the same mechanism may be used to cool the main pump and toempty or refill the operating reservoir in which parts of the operatingor control mechanism for th hydraulic motor may be disposed.

A further object of the invention is to provide an improved hydraulicsystem by which each of the above objects may be accomplished; whichwill require a minimum of additional apparatus; and which will becompact, dependable, simple and inexpensive.

Other objects and advantages will be apparent from the followingdescription of an embodiment of the invention, and the novel featureswill be particularly pointed out hereinafter in connection with theappended claims.

In the accompanying drawings:

Fig. 1 is a plan of the upper end of a hydraulic motor with controls andoperating mechanism applied thereto, and constructed in accordance withthis invention.

Fig. 2 is a face elevation of one form of a variable delivery,reversible type of hydraulic pump which may be advantageously employedfor operating a hydraulic motor in the apparatus of Fig. 1. v

Fig. 3 is a side elevation of a portion of the apparatus shown in Fig.1, but with parts broken away to show interior parts, particularly withrespect to the arrangement of the piping and certain of the valves; and

Fig. 4 is a schematic diagram illustrating a simple operating hydrauliccircuit for the hydraulic motor and the manner in which this inventionmay be applied thereto.

In the illustrated embodiment of the invention, the hydraulic motor, forthe control of which the system is designed, may be of any suitabletype, but that disclosed in my copending application, Ser. No. 492,526,above identified, is the type illustrated in the drawings. v

In apparatus of this type, the reservoir for the working fluid, such asoil, the pumps and the controls are all disposed at the top of thepress. The pumps, the valves, controls and piping are also largelydisposed within or just above the reservoir, so that any leakage willdrain directly into the tank. In such cases it is desirable to be ableto empty the reservoir when servicing the pumps, valves and piping isdesired. Accordingly, the usual reservoir is replaced by two separatereservoirs, an upper or top reservoir l0 (Fig. 3), and a lower orauxiliary reservoir l I, both of which are above the hydraulic motor.

The upper or top reservoir I0 is the normal or working reservoir inwhich as many as possible of the operating parts, such as the pump,valves and much of the piping are located. A pipe l2 opens from thebottom of the top reservoir l into the lower reservoir H, and isprovided with a valve l3 which is normally closed but may be opened inorder to drain oil from the top reservoir l0 into the lower reservoirII, when one desires to have access to the mechanism disposed within thetop reservoir ill. The valve [3 is normally closed except when onedesires to empty the top reservoir.

Disposed within the top reservoir I0 is a main pump it which has itsoperating or pump shaft extending through a packed opening or gland in awall iii of the reservoir 10, and outside of the reservoir It), the pumpis connected through a flexible drive It with a shaft ll of an electricmotor l8 or other suitable prime mover for the pump M. This pump M. maybe of any suitable type, but it is preferably of the variabledisplacementor variable delivery type, such as may be,

set or adjusted to create and maintain a desired pressure, even thoughno appreciable amount of fluid is passing through the pump. Thepressures in such pumps are frequently very high, and overheating of thepump becomes a problem.

The showing of the pump hi in Fig. l is more or less diagrammatic, butin Fig. 2 I have shown anelevation or face view of a pump it of asuitable type which can be used successfully as the main pump to operatethe hydraulic motor. Thistype of pump is known as a radial piston,variable delivery reversible pump, and it has a plurality of radiallydisposed pistons. Its pump shaft Ma is connected to the flexiblecoupling H at one end, and at its other end it extends into the pumphousing to operate the movable parts of the pump. This particular typeof pump has a relatively stationary pintle alined with the shaft,through which communication may be had with the radial cylinders, andconduits extend from the openings in the. pintle to positions near theperiphery of the pump housing, where they open into pipes l9 and 20.

Pumps of this type have a floating or shiftable member which, when in.central position, disposes the cylinders and pistons concentricallyabout the axis of rotation of the shaft I ia, so that the pump will notdeliver fluid under pressure in either direction. By shifting thisfloating member to one side into a position of eccentricity, it causesdelivery of fluid through one pipe, such as the pipe 19, and creates asuction in the other pipe, such as the pipe 2! When it is shifted in theother direction to the other side of its central position, or into anopposite position of eccentricity, it makes a suction pipe of the pipe[9 and delivers fluid under pressure through the pipe 20. Because ofthis characteristic, these pumps are also commonly known as reversible,variable delivery pumps, but they can be used as unidirectional deliverypumps.

The pump It has a closed housing, with a chamber 2! therein around themovable parts and the radial cylinders, and a pipe 22 is connectedthrough the pump housing into the lower part of this chamber 2|. Anoutlet pipe 23 is connected into the upper part of the housing tocommunicate with this chamber 2|.

Also disposed in the upper reservoir in is an auxiliary pump 24, such asa rotary vane type pump, secured to the wall l5 of the reservoir. andwith its operating shaft 25 extending outwardly through the wall l5where it is connected-v thi ugh a flexible coupling to. the shaft of anelectric motor 26 by which the pump 24 may be continuously driven. Theintake side of the pump 25 (see Fig. 3), is connected to a pipe 21,which extends outside of the reservoir l0 and connects to a valve 28,one branch of which is connected by a pipe 29 to a filter 30 disposed inthe lower part of the top reservoir H). The other branch of the valve 28is connected by a pipe 3| to a filter 32 disposed in the lower part ofthe lower reservoir H. By operating the valve 28, the intake pipe 21 ofthe pump 24 may be connected alternately and selectively to the lowerpart of either of the reservoirs Ill and II.

The output side of the pump 24 is connected by a pipe 33 to a choke orpressure relief valve 3%, which is in the nature of a pressure reliefvalve and creates a minimum back pressure on the pump 26. This choke 34is within the top reservoir l0, but it has an outlet extending throughthe wall l5 of the reservoir and then is connected by an elbow 35 to afilter 36, the other side of which is connected by pipe 3'! to one endof one channel through a heat exchanger 38. The other end of thatchannel extends through. a side wall of the top reservoir Ill, where itis connected to the pipe 22 that leads to the lower end of the chamberof the pump housing (see Fig. 2). The pipe 23 atv the top of the pumpdischarges back into. the reservoir it).

From the foregoing, it will be observed that the pump as withdraws fluidfrom the upper reservoir H), delivers. it. through the choke 34 to thefilter 36, then through one channel. of the heat xchanger 33 to thechamber in the pump housing, and from the pump housing it is returned tothe reservoir Ill. The other and separate channel of the heat exchanger38 is provided with connections 39 and 40 by which a heat exchangemedium, such as cooling water, may be passed in heat exchange relationto the fluid received through the pipe 31 and delivered into the pipe22. Heat exchangers of this type are well known in the art, andtherefore the details are not illustrated.

Included in one of the pipes 39 and 4D is a flow regulator 4| (Fig. 1),and in this illustrated eX- ample, this regulator is in series with thepipe 40, so that. all of the cooling water or suitable heat exchangemedium must flow through this regulator in an amount determined by thesetting of the regulator. well known in the art, and their details havenot been illustrated, but they have a valve member therein which isoperated by fluid pressure created in a duct 42. This duct extendsthrough a side Wall of the reservoir [0 and terminates in a thermal cell43 disposed within the reservoir H The varying temperature in thereservoir I 0 will produce a varying fluid pressure in the cell 43 andduct 42, which causes the valve in the flow regulator to open or closeto different extents, and thereby controls the rate of flow of thecooling wateror heat exchange medium through the exchanger 38. Thus, thefluid delivered through the. housing of the pump l4 will have itstemperature'controlled by operation of the flow regulator, which inturn, is controlled by the temperatureof the oil or fluid in thereservoir H).

The pipe 33 on the output side of the pump 24 has a duct 44 which leadsto the pilot-operated available for pilot operation of the controls ofthe,

hydraulic. motor. A simple hydraulic system These flow regulators arealso.

5 utilizing this invention is shown diagrammatically in Fig. 4.

The particular manner in which the pump l4 operates the hydraulic motoris not material to this invention, and any system of pilot-operatedcontrols for the ram or hydraulic motor may be employed. In Fig. 4 asimple hydraulic system with motor and pilot operation of the controlsis illustrated diagrammatically, but it will be understood that ifdesired a more elaborate system and controls, such as is disclosed in mycopending application Serial No. 492,526, hereinabove identified, may beemployed.

In this simple form and diagram shown in Fig. 4, the main pump l4operates to deliver fluid always in the same direction, and functions asa unidirectional pump. Its intake pipe 20 is connected to the reservoirl so as to draw operating fluid therefrom and deliver it under. pressurethrough the pipe l9 leading to a four-way or reversing valve 45. Pipes46 and 41 of valve 45 lead respectively to retracting and advancingchambers 48 and 49 in a cylinder 50 to create the hydraulic motor.Separating the retracting and advancing chambers 48 and 49 in a pistonsliding closelyin the cylinder 50 and having a reduced stem or ramportion 52 extending out of the cylinder 50 from the chamber 48 througha suitable packing gland, and carrying a platen 53 that moves toward andfrom a base 54, as the piston 5| reciprocates. By operating the valve45, the fluid under pressure from the pump may be delivered alternatelyto the motor chambers 48 and 49 so as to move the platen 53 back andforth. The valve 45 may have pilot devices 55 and 5B which operate thevalve element in the valve 45 between selected positions, and thesepilot devices are supplied with a pilot-operating fluid through pipes 51and 58 leading from a pilot control valve 59 which, in turn, is suppliedwith pilot-operating fluid through the pipe 44. The pilot control valve59 may be operated by a manual lever 60 or in any other suitable manner.

This is an extremely simple system, and often commercial installationshave a rather elaborate system of controls, such as for example,providing a control manipulated by the platen when it reaches a desiredposition in its return movement for setting the valve 45 to a positionin which fluid from the pump is by-passed back to the reservoir l8, andat the same time closing the pipe 46 to prevent escape of fluid from theretracting chamber 48. Such systems and controls are well known in theart, and their details have been omitted from this disclosure in orderto simplify the description of the device and prevent confusion with theimproved controls which form the subjectmatter of this invention.

The operation of the device is believed to be clear from the foregoingdescription, but will be briefly summarized. With both pumps I4 and 24operating continuously, and with the valve 28 set to draw fluid from thereservoir l0 and valve l3 closed, the fluid will be drawn from thereservoir l0 and delivered by the pump 24 under a minimum back pressure,partly to the pilot conduit 44, and the balance through the choke 34,filter 36 and heat exchanger 38 to the chamber 2| of the. main operatingpump l4, and then back to the reservoir through the pipe 23. When thetemperature of the oil increases beyond an undesired extent, the thermaldevice 43 will open the flow regulator 4|, allowing a cooling medium toflow through the heat exchanger from pipe 40 to pipe 39, and cool theoil delivered to the pump ing parts of the pump M will be kept below adesired maximum at all times, and a continuous source of pilot-operatingfluid under pressure will be available in the conduit 44. By operatingthe pilot valve 59, the reversing valve 45 may lice operated to causereciprocations of the platen If, for any reason, one desires to haveaccess to the pumps, valves and pipes that are contained within theupper reservoir Ill, the operation of the main pump I4 is stopped, suchas by shutting off its operating motor, and the valve I8 is then openedwhich allows the fluid to pass by gravity from the reservoir ID to thereservoir After the servicing has been completed, valve I3 is closed,the pump 24 alone is operated, and the valve 28 is operated to connectthe pipe 3| to the pipe 2'|. The fluid is then withdrawn from the lowerreservoir H and passed through the chamber 2| of the main pump l4 intothe tank It], which soon transfers all of the fluid from the reservoir Hback into the reservoir it. After that has occurred, the valve 28 isoperated to reconnect the pipes 21 and 29 and the device is ready for anew operation.

A pressure responsive switch 6|, Fig. 1, may be connected to elbow 35 soas to be caused to operate if the pressure exceeds a predeterminedpressure, and it controls wires of a circuit through a battery 62 and asignal 63. The signal is operated whenever the filter 35 becomes cloggedor plugged and increases the back pressure, to warn the attendant thatthe filter must be cleaned.

A temperature responsive switch 64 has a heat responsive cell within thereservoir Ill and it similarly closes a circuit through a danger signal68 if the temperature of the oil in the reservoir H] gets too high forany reason.

It will be observed from the foregoing that this transfer of fluidbetween the reservoirs is accomplished in a relatively simple manner byusing gravity or the same pump which supplies the pilot operating fluidand cools the main pump, and at the same time the overheating of thepump is prevented in a simple manner by automatic means. This cooling ofthe main pump very deflnitely improves the operation and life of suchpumps.

It will be understood that various changes in the details andarrangement of parts, which have been herein described and illustratedin order to explain the nature of the invention, may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the appended claims.

I claim:

1. In an operating control for a hydraulic motor including said motorwith its controls, a main pump with a closed housing enclosing theworking elements, a reservoir, and piping'connecting the reservoir, pumpand motor to form an operating hydraulic system for said motor, thatimprovement which comprises the combina-'- tion therewith of anauxiliary pump connected at its intake side to said reservoir, a heatexchanger having a passage in which a fluid may be cooled and connectedat one end to the output side of said auxiliary pump and also havinganother passage through which a cooling medium is passed, a conduitconnecting the oth end. of said pa sa e or sa d: ex an er to. one sor tsaid numohousins; to convey the. ecr tin f uid; from. the. aim l arvaunts. that; has .5 hr u h said. iiqb dl fi f 9. id. P p. housin a. pasa e. c nn ctedo s id aux; ar 1 .14.1119. an eadin to. said contro s. tofurnish. operativ pilot. i uid thereto. oon r ndu t onnect ng. e positeer Qt. ci. BR1 19 1 0 1 5 nsv to, said. r serv ir a d a thermllycontroll d elemen re p nsive. to he temperature o the. oil in saidreservoir for regulating the flow or eooiing medium throughsaidexchanger, to pass ncre sed. co l n m dium throu h a d changer withincreased temperature of the oil said reserv In an operatin contro for ahydrauli motor including said motor with its controls, a main-pum it a.lo e ho sin en l sin the. wo king lements, a res rvoir. and pipin csnneti h reser oi owns d motor to form an operating hydraulic system forsaid motor, that improvement which comprises the combination therewitl'v of an auxiliary pump connected at its intake side to said reservoir, aheat exchanger having apassage in which a fluid may be cooled andconnected at one end to. the. output side of said auxiliary pump andalso having ano r p a e. hrough which a coolin medium is passed, vaconduit connecting the other end of; said passage of. said exchanger toone part of said pump. housing to convey the operst n fluid fr mth a xliary p mp that pa es through said exchanger to said pump housing,another conduit connecting the opposite part of said pump housing to.said reservoir, a choke inthe connection from the auxiliary pump to saidexchanger, a take ofi pipe for supplying fluid under pressure to fluidoperated controls forv said motor, connected to the output side of saidauxiliary pump before its connection to said choke, and a thermallycontrolled element responsive to the temperature of the oil in saidreservoir for regulating the flow of cooling medium through saidexchanger, to pass increased cooling medium through said exchanger withincreased temperature of the oil in said reservoir.

3, In an operating control for a hydraulic motor including said motorwith its controls, a main pump with aclosed housing enclosing theworking elements, a reservoir, and piping-con nesting the reservoir,pump and motor to form an operating hydraulic, system for said motor,that improvement which comprises the combination therewith of anauxiliary pump connected at its intake side to said reservoir, a heatexchanger connected to the output side of said auxiliary pump, a conduitconnecting said exchanger to one part of said pump housing to coonveythe operating fluid from the auxiliary pump that passes through saidexchanger to said pump housing, a passage connecting the output side ofsaid auxiliary pump and saidcontrols to supply thereto operating pilotliquid, another conduit connecting the opposite part of said pumphousing to said reservoir, and a regulator for the activity of saidexchanger having a heat responsive control element disposed in heatresponsive relation to the fluid in said reservoir whereby the activityof said heat exchanger will be automatically responsive to thetemperature 1e operating fluid in said reservoir.

lie mo" main crating 8. some a. c enched: nin co n ctin the intake sideof said auxiliary pumgtgthe; l w Wi Q each. i; ai Q .Y l E S RGE valv inai pi e n op n. .ee to. connect said; rs! sumo al a s ndsel ctivelv to.aid

a. p e e. d et valve: th out ut said. au ump, or rea ng a lse sir d p peleadin from the output sid of the. auxi i. pum bsiqres on. tosaid relif. valve. or supply n one .uiii. to. aid IAUZDlfi. I AQMJS, Q ILDQ Q, tosaid reliei valve for fluid therefr in in heat exchanging relation to,sa1d-,mai and then to, one or: said reservoir-s ad m a for varyingthetempe at re of the. fluid passing from said relief valve tosaid-melanoma.

5. In an operating control for ahydralllicmd-n tor including said,motor, its controls. and a; main pump, that. improvement. which,comprises; a Working reservoir, aseparate stora e lefifllfvoiri. anauxiliary pump, abranched pipe connecting the intake side 01 saidauxiliary. pump. to the; lower part of each of said reservoirs, aselector.- valve in said pipe. and operating to. connect; said auxiliarypump alternately and selectivnlyl, to said reservoirs, means in theoutputv side, Qfi' said auxiliaryv pump for creating a desired bach,pressure, a pipe leading. fromthe outputside oi the auxiliary pump.before. its, connection to said means, for supplying operating: fluid tosaid controls, means connected to said previous means; for passing fluidtherefrom in heat exchanging relation to said main pump and then to oneof said reservoirs, means for-varying the temperature of the fluidpassing from said first means;

working fluid to said motorand having a closed housing with achannelaround the. com-pressing parts, a reservoir, anauxiliary:pumpconnected at its intake side tosaid reservoir, means con-unected to the output side of said auxiliary-pump to. create a minimumbackpressure, a conduitleaving the output side of the pump before itsdelivery to said means for supplying operating; fluid. under pressurefor the motor controls, a heat exchanger having one channel connected atone end: to said meansand atitsothenend to said channel in said housing,thehousinghaving a drain forits channel baclc to said reservoir,connections tor the other channel'of said exchanger toenable. a coolingmedium tohe passed therethrough, a regulator in said other channel ofsaid: exchanger for controlling fluid flow therethrough, and a thermallyresponsive element disposed in. said reservoir was to be responsive tothe temperature of the-operating fluid therein, and controlling saidregulator whereby, the temperature of said mainpump can be controlledand a pilot fluid supplied for operating the controls of said member.

7.. In a hydraulic system for a hydraulic motor and its. controls, amain pump, for supplying working fluid to said motor, and having avclosed; housing with a. chamber in heat exchangingrelation to. theworking parts, and separatefrom its, working compartment, a reservoir;an auxin. iary pump, connected at its, intake. side to. reservoir, aheatexchanger having: one channel. thereofconnected at one end to. saidswells.

iary'pump arid atitsother end'to said. chamber of said pump housing, andhaving its other channel formed for connections by which aheatexchanging medium may be circulated therethrough to modify thetemperature of the working fluid delivered by said auxiliary pump, and aflow regulator in said other channelby which the rate of heat exchangewith said working fluid delivered to said main pump chamber may bevaried, said pumphousing having another part of its chamber connectedtosaid reservoir, whereby the fluid delivered by saidauxiliary pump willbe circulated through said pump housing and returned to said reservoir.

8. In a hydraulic system for a hydraulic motor and its controls, a mainpump for supplying working fluid to said motor, and having a closedhousing with a chamber in heat exchanging relation to the working partsand separate from its working compartment, a reservoir, an auxiliarypump connected at its intake side to said reservoir, a heat exchangerhaving one channel thereof connected at one end to said auxiliary pumpand at its other end to said chamber of said pump housing, and havingits other channel formed for connections by which a heat exchangingmedium may be circulated' therethrough to modify the temperature of theworking fluid delivered by said auxiliary pump, and a flow regulator insaid other channel by which the rate of heat exchange with said workingfluid delivered to said main pump chamber may be varied, said pumphousing having another part of its chamber connected to said reservoir,whereby the fluid delivered by said auxiliary pump will be circulatedthrough said pump housing and returned to said reservoir, said fluidregulator having a thermally responsive, operating element disposed inheat exchanging relation to the fluid passing through said reservoirunder the impulsion of said auxiliary pump.

9. In a hydraulic system for a hydraulic motor and its controls, a mainpump for supplying working fluid to said motor, and having a closedhousing with a chamber in heat exchanging relation to the working partsand separate from its working compartment, a reservoir, an auxiliarypump connected at its intake side to said reservoir, a heat exchangerhaving one channel thereof connected at one end to said auxiliary pumpand at its other end to said chamber of said pump housing, and havingits other channel formed for connections by which a heat exchangingmedium may be circulated therethrough to modify the temperature of theworking fluid delivered by said auxiliary pump, and a flow regulator insaid other channel by which the rate of heat exchange with said workingfluid delivered to said main pump chamber may be varied, said pumphousing having another part of its chamber connected to said reservoir,whereby the fluid delivered by said auxiliary pump will be circulatedthrough said pump housing and returned to said reservoir, said fluidregulator having a thermally responsive, operating element extendinginto said reservoir so as to operate said flow regulator in response tofluctuations in the temperature of said fluid in said reservoir.

10. In a hydraulic system for a hydraulic motor and its controls, a mainpump for supplying working fluid to said motor, and having a closedhousing with a chamber in heat exchanging relation to the working parts,and separate from the working compartment, a reservoir, an auxiliarypump connected at its intake side to said reservoir, a heat exchangerhaving one channel thereof connected at one end to said auxiliary pumpand at its other end to said chamber of said pump housing, and havingits other channel-formed for connections by which a heat exchangingmedium may be circulated therethrough to modify the temperature of theworking fluid delivered by said auxiliary pump, a flow regulator in saidother channel by which the rate of heat exchange with said working fluiddelivered to said main pump chamber may be varied, said pump housinghaving another part of its chamber connected to said reservoir, wherebythe fluid delivered by said auxiliary pump will be circulated throughsaid pump housing and returned to said reservoir, a filter in serieswith the channel of said heat exchanger connected to said auxiliarypump, and a pressure responsive switch connected to the connectionbetween said filter and said auxiliary pump, and operated by fluiddelivered by the pump if it exceeds a predetermined pressurenormally'sufficient to cause free circulation of fluid through said pumphousing, such as by a high back pressure that might be due to cloggingof the filter, and circuit wires controlled by said pressure switch.

11. In a hydraulic system for a hydraulic motor and its controls, a mainpump with a working chamber for supplying working fluid to said motor, apair of reservoirs disposed at different levels, a pipe leading from theupper reservoir to the lower reservoir, a valve in that pipe selectivelyoperable to allow the upper reservoir to drain into the lower reservoir,an auxiliary pump having two connections at its intake side, one to thelower reservoir, and the other to the upper reservoir, a valve operableto connect said auxiliary pump at its intake side alternately andselectively to said reservoirs, a passage connecting the output side ofsaid auxiliary pump to said controls to supply operating pilot liquidthereto, said controls having an exhaust to said upper reservoir, aconnection from the output side of said auxiliary pump back to saidupper reservoir, whereby fluid may be transferred in either directionbetween said reservoirs, and a connection between the working chamber ofsaid pump and said upper reservoir whereby said reservoir serves bothpumps.

12. In a hydraulic system for a hydraulic motor and its controls, a mainpump with a working chamber for supplying working fluid to said motorand a cooling passage therethrough, a pair of reservoirs disposed atdifferent levels, valve controlled means for draining the contents ofthe upper reservoir into the lower one, an auxiliary pump having twoconnections at its intake side, one to the lower reservoir, and theother to the upper reservoir, a valve operable to connect said auxiliarypump at its intake side alternately and selectively to said reservoirs,a connection from the output side of said auxiliary pump back to saidupper reservoir through said pump cooling passage, whereby fluid may betransferred in either direction between said reservoirs, and aconnection between the working chamber of said main pump and said upperreservoir whereby said reservoir serves both pumps.

13. In a hydraulic system having a hydraulic motor, a main pump with aworking chamber for supplying working fluid to said motor, a mainreservoir having a liquid capacity suflicient ;to serve fiully saidmotor and pump, and connections with controls, between the pump, rho--tor and-reservoir to form a hydraulic circuit, that 'improyement whichcomprises the combination therewith oi second resorvoir of sufiicientsize to receive and hold all of the liquid from said main pump'to thelower parts of said reservoirs alternately, and means connecting theoutput side of said auxiliary pump to said controls and through saidcontrols to said upper reservoir.

14. Ina hydraulic system having a hydraulic motor, a .main pump with aworking chamber for supplying working fluid to said motor, a mainreservoir having a liquid capacity suiiici'ent to serve .fully saidmotor and pump, and connections with controls, between the pump, motorand reservoir toform a hydraulic circuit, that improvement whichcomprises the combination therewith of a second reservoir of suflicientsize to receive and hold all of the liquid from said main reservoir anddisposed at a lower level than said main reservoir, a valve controlledconnection for directly draining the main reservoir into said secondreservoir, an auxiliary pump, means for connecting the intake side ofsaid auxiliary pump to the lower parts of said reservoirs alternately,means-connecting the out- 12 put-side oi said auxiliary pump to saidupper reservoir, a pressure relief valve in said. last connectingmeansior creating a back pressure, on

said auxiliary .pump, and a connection from. the output side of theauxiliary pump before said relief valve, for supplying pilot operatingfluid to said controls.

THOMAS F. STACY.

REFERENCES CITED The following references are 'of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,411,802 Mosher Apr. 4, 19221,855,032. Sinclair Apr. 19,1932 2,123,391 Whitfield July 12-, 19382,196,350 Ahart Apr. 9, 1940 2,210,121 Jewell Aug. 6, 1940 2,232,103Ernst et a1 Feb. 18, 1941 2,242,209 Dinzl May 20, 194-1 2,254,917Schrdder Sept. 2, 1941 2,296,325 Bak Sept. 22, 1942 2,306,379 ConradsonDec. 29, 1942 2,357,019 Nowak Aug. 29', 1944 2,358,949 Trautman Sept.26, 1944 FOREIGN PATENTS Number Country Date 511,859 GreatBritain Aug.25, 1939

